The production of PAS for a variety of industrial and commercial uses is known. PAS is moldable into various articles including, but not limited to, parts, films, and fibers by means of, for example, injection molding and extrusion molding techniques. These articles have been employed in a variety of fields where heat and chemical resistance properties are desired. For example, PAS is utilized as a material for preparing electrical and electronic parts and automotive parts.
Lower molecular weight PAS compounds comprising PAS oligomers contained in PAS polymer product can cause the product to have relatively poor mechanical properties. Therefore, a relatively high oligomer content in the PAS product is disadvantageous in molding and other process applications. In addition, when the PAS product is melted, these lower molecular weight compounds can volatilize and can produce undesired off-gassing.
It has been found that certain extraction agents, such as, for example, N-methyl-2-pyrrolidone, hereinafter referred to as NMP, can successfully remove oligomers from PAS. However, the PAS can become imbibed with an extraction agent. For example, upon addition of NMP to poly(phenylene sulfide), hereinafter referred to as PPS, PPS can absorb NMP up to about 1.5 times its weight.
Various techniques have been utilized to remove extraction agents, but these techniques have disadvantages. For example, water washing to remove extraction agents from PAS can produce large quantities of extraction agent laden wastewater that must be reclaimed due to environmental and economic considerations, thereby increasing equipment and energy costs for production of PAS.
There is a need in the PAS industry for a process to produce PAS having a higher molecular weight, i.e., a lower oligomer content. In addition, there is a need for processes effectively to remove extraction agents from PAS to produce the most economical and highest quality PAS.